Fluid supply systems use motors to drive pumps and transfer fluids from supply reservoirs, such as wells, to demand reservoirs, such as tanks. A sensor measures a characteristic of the fluid, and a controller controls operation of the motor. In some systems, the controller measures a level of the fluid in a tank and controls operation of the motor to maintain the level within a range. When the level reaches the low end of the range, the controller turns the motor on and keeps it on until the level reaches the high end of the range.
In other systems, the speed of the motor is controlled to maintain a fluid characteristic within predetermined parameters. Variable speed controls can gradually increase or decrease the pumping rate and thereby reduce the variability of the fluid characteristic. However, many single phase systems currently in operation were not designed to operate at a variable speed and may not be capable of doing so. In many instances, variable speed control of single phase motors magnifies the perceived acoustic noise generated by torque pulsations making it unacceptable to some users. While it is desirable to provide a variable speed system capable of operating with a variety of motors in new and retrofit applications, it is also desirable to reduce or eliminate torque pulsations resulting from variable speed operation of single phase motors. More generally, it is desirable to control motors to reduce the variability of system characteristics such as speed, torque, fluid pressure and noise.